1. Field of the Invention
The present invention relates to a key input device which generates a key code in response to an operation of a user.
2. Description of the Related Art
A key input device (key matrix device) is known. For example, a keyboard of a computer, a keypad of a calculator, keypads of a remote control device, an electronic lock, etc. are equipped with the key input device. The key input device generates a data and an instruction in the form of a key code in response to an operation of a key switch, and outputs the key code to a processor. The key input device has a key matrix section and a control section. A plurality of key switches are arranged in a predetermined array in the key matrix section. The control section performs a key scan operation to monitor the operation of any of key switches and to detect the position of the operated key switch.
The key input device is demanded to have a miniature size, a light in weight, advanced functions, and so on (see JU-A-Showa 62-138237, and JP-P2001-255983A). The control section is generally composed of an integrated circuit. For this reason, there is a case that the number of terminals of the integrated circuit is restricted, by which key signals from the key matrix section are received. Therefore, a technique is demanded for attaining the advanced function of the key input device without increasing the number of terminals of the integrated circuit.
FIG. 1 is a block diagram showing a configuration of a key input device described in Japanese Laid Open Utility Model application (JU-A-showa 62-138237) as Related Art 1. Referring to FIG. 1, the key input device is provided with two of first and second key matrix circuits 101 and 102. The first key matrix circuit 101 is provided as standard equipment, and the second key matrix circuit 102 is provided for extension. A control section 106 simultaneously searches the both matrix circuits. This control section includes a search section and a matrix circuit determining section. The search section simultaneously outputs one or a plurality of scan signals of different phases from one or a plurality of common scan output terminals to the both matrix circuits. The search section simultaneously scans the both matrix circuits, and a scan signal passing through the operated key switch of the both matrix circuits is supplied to a common scan input terminal. Moreover, the matrix circuit determining section samples the scan signals at a predetermined time from the output of the scan signals, and compares a signal level of each of the sampled scan signals with a threshold level to determine the operated key switch of the key matrix circuit.
Here, in the key input device in the Related Art 1, output terminals of the first key matrix circuit 101 for scan signals are respectively connected to the common scan input terminals, and also output terminals of the second key matrix circuit 102 for scan signals are respectively connected to the common scan input terminals. The key input device in the Related Art 1 is also provided with: distinction side diodes for backflow prevention having anodes respectively connected to the output terminals of scan signals of the second key matrix circuit 102; and an integrated circuit (IC) 106 that holds the high level of cathodes of the distinction side diodes for a period longer than a predetermined time period in a delayed manner to achieve application to the predetermined terminal.
In the key input device of Related Art 1, when a key switch of the first key matrix circuit 101 is operated or pushed down, a scan signal passing through the key switch is supplied to the common scan input terminal. At this time, the scan signal is not supplied to the distinction side diode due to blockade by the search side diode, so that the cathode of this distinction side diode is held at a low level. When a key switch of the second key matrix circuit 102 is pushed down, a scan signal passing through this key switch is supplied to the common scan input terminal through the search side diode and also supplied to a signal holding circuit through the distinction side diode. At this time, the cathode of the distinction side diode is held at a high level based on the high level of the scan signal for the predetermined period from the leading edge by the signal holding circuit. Also, this cathode becomes high for the predetermined period for sampling by the matrix circuit determining section.
With this configuration, the above-mentioned technique achieves a key input device that, when the first key matrix circuit 101 and the second key matrix circuit 102 are simultaneously scanned to determine the operated key switch of the key matrix section in an operation of the plurality of search side diodes (Da to Dh), the distinction side diodes (Da′ to Dh′), and the integrated circuit 106.
The above-described key input device requires a plurality of diodes as its components for determining operated key switch in the first key matrix circuit 101 and the second key matrix circuit 102.
FIG. 2 is a block diagram illustrating a configuration of a key input device disclosed in Japanese Laid Open Patent Publication (JP-P2001-255983A) as Related Art 2, Referring to FIG. 2, the key input device can detect more pushed-down key switches in a same number of terminals, by adding a simple hardware circuit. When a pulse signal is supplied from one of lines, signals are outputted from all the other lines in accordance with key states. Thus, while sequentially scanning the lines, the key input device detects pushed-down states of key switches K00 to K55.
The key input device described in JU-A-Showa 62-138237 can perform the key scan for a large number of keys, but requires a plurality of diodes as its components in order to determine the pushed-down key. Therefore, it is desired to provide technique for reducing the number of circuit components of the key matrix part.
Recently, a key input devices with small size is demanded to achieve power consumption reduction. For this purpose, normally the key scan operation is stopped and the key scan operation is started in response to a key operation as a trigger.
The key matrix part of the key input device described in JP-P2001-255983A requires a plurality of diodes to determine a pushed-down key, but the number of components is less than those of the key input device described in JU-A-Showa 62-138237. However, in the key input device described in JP-P2001-255983A, once the key scan stops, it is difficult to newly start a key scan by detecting the pushing-down of any of all the keys.